The Circle of Life
Viruses are
present throughout the global oceans contributing to the lysis of marine microbes,
influencing the number of bacteria, phytoplankton and cyanobacteria, and
releasing organic carbon into the oceanic carbon cycle. The South Pacific coral
reef viral community displays spatiotemporal variability, the specifics of
which are examined in Burkepile et al,
2014. The spatiotemporal changes in the viral community in turn cause variances
in the numbers and structure of the microbial community within the South Pacific
coral reef.
The study by
Burkepile et al (2014) was conducted within
the French Polynesia during the dry season of August 2013, observing the
microbial community and its structure. In order to examine biotic and abiotic
variables, water samples were collected at four different reef locations
periodically along the same transect lines. Once taken back to the laboratory,
using flow cytometry the samples were analysed by separating different
heterotrophic bacteria, phytoplankton and viruses into subsets. The purpose of
this method was to calculate the abundance of virus, bacteria and phytoplankton
at the four different sites, and to assay viral abundance (VA) and lysis at
different locations and times.
The examination
of microbial abundance within the coral reef locations resulted in identification
of high spatial heterogeneity, yet low temporal variation in viral abundance
and lytic activity. There were differences among the sites investigated, with
one of the sites exhibiting continuous viral abundance and infection through short
term temporal analysis. The highest levels of VA, lysis and microbial host
abundance were measured at two sites. One of these sites experienced run off
from a nearby agricultural area which would add to the availability of
nutrients permitting increased numbers of microbial hosts and viruses. The
second of these sites was the fringing reef, which being closest to land and in
the shallowest water may have obtained higher levels of nutrients from
terrestrial run off and benthic upwellings.
The data
shows that the increase in VA and viral lysis adds to the DOC pool to a
considerable level, at some sites even up to 90%. The range in mortality of
heterotrophic microbes through viral lysis is vast, with the study suggesting
figures of 24-367%; the large range may be so vast due to the variation in VA
and microbial host abundance between different sites. The study concludes that “viruses
have a key role in both top down and bottom up control of microbial communities
in coral reef waters”. A great deal of data is produced from the study to
support this conclusion, and other previous studies have similar findings again
reinforcing the conclusion. However, there are issues with some of the
methodologies used within the study. The method of flow cytometry (FC) for the
identification of the viruses could be questioned, as the genetic identity of
the viruses could not be confirmed. This may have led to small discrepancies in
categorising the subsets and consequently the data. Further study into the
level of inaccuracy may need to be evaluated before making a final judgement upon
the study’s conclusions.
A literature
review of the role of viral lysis as a contributor to the marine nutrient cycle
in coral reef ecosystems could be beneficial in coming to a further conclusion.
The nutrient input from environmental and anthropogenic sources may be an even
greater influence on the nutrient cycle in these waters. This, however, is
difficult to judge as the viral, bacterial and plankton abundance varies
between different reef sites, along with different types and levels of environmental,
biological and anthropogenic variables. Additional factors influencing microbial
abundance within the coral reefs include; increased proximity to predatory organisms
and increased nutrients from benthic organisms. With this many abiotic and
biotic influences it is difficult to determine exactly how much of a
controlling influence the VA and viral lysis actually have on the nutrient
input of the coral reef ecosystem. Additional investigation over a greater period
of time, and at numerous different geographic sites, with emphasis on the
impact of external factors would be greatly beneficial to identifying the extent
of VA and viral lysis. Although, this study does provide a great base to the role
of viruses as prominent features of the coral reef nutrient cycle.
Burkepile, D.E., McMinds, R., Payet, J.P. and
Vega Thurber, R.L. (2014) Unprecedented evidence for high viral abundance
and lytic activity in coral reef waters of the South Pacific Ocean. Frontiers in Microbiology. 5, No. 00493.
Interesting paper that supports the role of virus in microbial mortality and nutrient cycling in the coral reef. It is an interesting ideal that maybe this could be a solution to oilgotrophic water. Similar to the ideal of "fertilizing" the water with nutrient, just that this could be a self-sustainable solution. Well, it's just a thought, maybe it might not be even practical at all.
ReplyDeleteHi Emma
ReplyDeleteI hadn't appreciated how much viral lysis could contribute to the DOC pool in tropical coral reef ecosystems. I can understand the reasoning of the authors conducting the study during the dry season to look at the system with base level inputs of nutrients. I do think, however, that a follow up study comparing lytic activity in the wet season with the dry system would be useful in ascertaining how nutrient inputs into the ecosystem effect viral lysis, with more nutrients entering the ecosystem via runoff. What do you think?
I like the idea of this Li, however, I think further information would need to be gathered before this consideration could be made. With the variation in anthropogenic nutrient input within different areas it may be difficult to know where and what level of viral number could be added/increased. I think it would be great to have a natural answer to oligotrophic waters though.
ReplyDeleteI completely agree with your thoughts Anita, the lytic activity within the wet season may vary greatly due to more water carrying additional nutrients into the oceans. A study which compares the sites through different seasons could give a more appropriate insight into the ecosystem effects throughout the years.
ReplyDelete